What is the centripetal acceleration of the hammer in circular motion?

[Coco12]

Homework Statement

An athlete whirls a 7.00 kg hammer tied to the end of a 1.3 m chain in horizontal chain. The hammer makes one complete revolution in 1.0 s.
(A) What is the centripetal acceleration of the hammer? 51 m/s2

Homework Equations

ac=4pi^2*r/r^2

The Attempt at a Solution

I know the formula for centripetal acceleration is as above. but how is the answer 51?
I put it in my calculator and did not get that...
4(3.14^2)(1.3)/1.3^2)

What am i doing wrong??

 

[tiny-tim]

Hi Coco12!

ac=4pi^2*r/r^2

No, centripetal acceleration = ω²r = v²/r